Climate System and Meteorology

Geophysics describes the physics of the Earth and its environment. It includes the Earth's internal structure, its composition and tectonics, volcanism and rock formation, oceanography, meteorology, atmospheric physics and hydrology. NILU conducts research on a range of topics related to the geophysical climate system, such as soil moisture, atmospheric water transport and circulation, meteorology and cloud optical properties.

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Atmospheric circulation and "teleconnections"

Global atmospheric circulation patterns are very complex. Atmospheric variability in one region can often affect the climate in areas located several hundred miles away. Such phenomena are often called “teleconnections”. One well-known phenomenon is ENSO (El Niño-Southern Oscillation), which describes the relationship between air pressures in Tahiti and Darwin. Another pattern is NAO (the North Atlantic Oscillation), which strongly influences the climate in Europe and Scandinavia. A positive NAO index describes a situation with above normal high pressure around the Azores and a corresponding strong low-pressure situation around Iceland.

At NILU there is a focus on large-scale circulation patterns and their impact on various climate parameters – from sea ice to stratospheric ozone. The Arctic and Northern areas have been a key area for studies of the changing climate. Observations during the last decade have indicated that the sea ice is melting much faster than most climate models predict. This ice melting might be related to increased cyclone activities in the Northern areas during the summer.

A key task at NILU is to identify climate variability caused by natural phenomena and anthropogenic influences. The climate variability we observe is always affected by both factors.

Atmospheric water transport

Atmospheric water transport from remote areas might contribute to episodes of extreme precipitation over Norway. This can happen through atmospheric “rivers” that are induced by cyclones at mid latitudes.

NILU is conducting ongoing research on the physical properties, structure and strength of this water transport. The work is important for understanding the impact of sea surface temperature (SST) on extreme precipitation and the climatological origin of precipitation in Norway and the North. This will provide important knowledge about the connection between climate change and extreme weather events.

Land data (temperature, snow, assimilation (LDAS))

Land data (temperature, snow, assimilation (LDAS))
Soil moisture, snow and soil temperature are geophysical parameters that have a substantial impact on vegetation and climate. These parameters will influence plant transpiration and photosynthesis and will have a significant impact on the Earth’s hydrological cycle. Variations and trends in soil moisture will reflect changes in precipitation and radiation and will contribute to climate feedback mechanisms on a local, regional and global scale.

At NILU we have developed a land data assimilation system (LDAS) in cooperation with the Norwegian Meteorological Institute ( and Meteo France. The system is based on different variants of the Ensemble Kalman Filter (EnKF) and Extended Kalman Filter (EKF) and is linked to the offline SURFEX land data model (Le Moigne, 2009; Mahfouf et al., 2009). Soil moisture from AMSR-E, ASCAT and SMOS are used in the assimilation. The system can provide important information about soil moisture, snow and surface temperatures in Scandinavia and Europe. We also aim to integrate LDAS into meteorological weather prediction models to improve the weather forecast.

Clouds and radiation

Clouds have a large impact on climate. They can reflect solar radiation back to space and consequently cool the Earth’s surface. Clouds can also absorb infrared radiation (IR) from the Earth and emit some of this radiation back to the Earth’s surface, which enhances the greenhouse effect. The combined effect of these two phenomena, i.e. the cooling effect from reflection of solar radiation and the warming effect from absorption of IR, determines whether certain types of clouds will have a net cooling or warming effect. High thin cirrus clouds will typically have a warming effect, whereas low thick clouds will cool the Earth.

It is scientifically challenging to describe how clouds will respond to a temperature increase induced by human activities. Increased global temperature might enhance evaporation, which might increase cloud formation. The question is whether these additional clouds will have a cooling or warming effect.

Research at NILU related to this topic addresses the climate effect of cirrus clouds. These clouds are located at altitudes with very low temperature, often below -40C, where the clouds consist of ice crystals with different shapes. The sizes and shapes of the ice crystals will depend on the temperature, humidity and the concentration of aerosols in the atmosphere. A good description (parameterization) of cirrus clouds is important for climate modelling and predictions of future climate. Through the NORCLIM project, NILU is involved in the development of a climate model (NorESM) in cooperation with several other national partners.